Writing instruments embodying the design of my said U.S. Pat. No. 4,185,933 have been widely manufactured and sold by me and various licensees. The commercial success of this flat two-cartridge pen has stimulated price competition. This flat type of pen, as shown in the patent drawings, is now sold world-wide and, while it has not been imitated, it does have price competition from multicolor pens, which are sold in large quantities. To remain competitive I must reduce the cost of my pen, which is primarily based on labor for assembly and secondarily on the cost of the parts.
Referring to my U.S. Pat. No. 4,185,933, the writing instrument has two cartridges, preferably of different color, and these are projected from the tip of the pen body selectively. A tension (expansion) spring is used to retract a cartridge when it is desired to place the pen in a pocket or to change colors. This tension spring must be manually attached to each side or glide to effect this retraction. This is a substantial element of labor cost.
Also, the spring for biasing the clip of the pen had to be glued on one end to a stationary part of the pen and the other end ultrasonically staked to the back side of the clip.
Furthermore, the body of the pen of U.S. Pat. No. 4,185,933 was formed in two longitudinal halves, and these two pieces had to be welded together. Ultrasonic welding was employed, requiring an additional labor step as well as capital expenditure for the equipment.